The chief objective of this renewal application is the study of the structure-activity relationship of beta-endorphin and related psychopharmacologically significant peptides. We propose to synthesize analogs of beta-endorphin by the solid-phase method for the following objectives: (a) analogs with unique biological (behavioral) activity without analgesic potency, (b) enhancement of opiate and behavioral activities but no narcotic addiction, such as tolerance and physical dependence, and (c) determine essential residue(s) in beta-endorphin to biological activity. In addition, we plan to isolate and characterize the beta-endorphin receptor in the bovine and rat brain. Isolation and characterization of beta-endorphin-like peptides in pituitary glands of turkey, frog and other species as well as in bovine brains are also part of this proposal. It is also planned to isolate and characterize the beta-endorphin receptor from neuroblastoma x glioma hybrid cells.